Severe, corticosteroid-insensitive asthma is observed in ~ 10% of the asthma population but accounts for the majority of the morbidity, mortality and cost associated with the disease. For nearly 10 years our group has studied airway redox disturbances in adults and children with asthma through the NIH/NHLBI Severe Asthma Research Program (SARP). Through innovative metabolomics and redox biochemistry, methodologies that are a strength and unique to our collaborative efforts, we identified clinically relevant phenotypes of asthma. The phenotypes are defined by biomarkers specific to underlying biochemical mechanistic abnormalities, including eosinophil-mediated oxidation, depletion of antioxidants and protective airway S-nitrosothiols, and airway acidification. Here, we propose to study a new component that is informative for longitudinal assessment of severe asthma phenotypes: gender effects. Severe asthma affects boys more than girls; however, severe asthma in adults is a disease of women. The age-dependent change in gender predilection is one of the largest signals in severe asthma epidemiology, but remains understudied. We reason that identification of the metabolic mechanism(s) underlying onset of severe asthma in young women during adolescence, and resolution of severe asthma in boys, will reveal fundamental pathophysiology of severe asthma. Importantly, we aim to develop clinical testing procedures to accurately assign metabolic asthma phenotypes; and to follow patients in each phenotype to uncover clinical longitudinal outcomes. At the conclusion of the project, we anticipate that we will have 1) developed clinically relevant tests to identify severe asthma phenotypes; 2) determined the longitudinal outcome of the phenotypes; and 3) identified the mechanisms underlying the preponderance of women in the severe asthma population.